Add tag parser for Markdown files

[InAnYan]

Is your feature request related to a problem? Please describe.
Imagine one needs to write an ADR (Architecture Decision Record) for a dsn artifact. And one uses Markdown for that.

But it seems that OFT doesn't support tag parsing from Markdown files.

Describe the solution you'd like

Support using Markdown for both describing requirements and to be required.

Describe alternatives you've considered
I think none, but I might complicate or miss something.

Additional context
None.

[redcatbear]

I just reproduced this issue. Will add the missing parser feature soon.